The Armstrong plate. Relief from Copernicus GLO-30; rivers and lakes from USGS NHD; watersheds from the USGS Watershed Boundary Dataset; roads and city limits from Census TIGER 2024.
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Armstrong’s center stands about 590 ft above sea level. Within three miles the land runs from 550 ft to 750 ft, a difference of 200 ft: rolling country. The highest named summit within 15 miles is Caddo Hills, about 830 ft, 5 miles east-northeast.
Under the town center the state geologic map shows Alluvium (fine-detrital), from the Holocene, less than 12,000 years old.
The section below crosses 4 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 64×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Claystone. Age: Early Cretaceous, 100 to 145 million years old. About 18 mi of the line.
Fine-detrital. Age: Holocene, less than 12,000 years old. About 4 mi of the line.
Limestone, shale, marlstone. Age: Early Cretaceous, 100 to 145 million years old. About 1 mi of the line.
Marlstone. Age: Early Cretaceous, 100 to 145 million years old. About 0.4 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
Heights from Copernicus GLO-90 (a surface model: it includes buildings and tree canopy); summits from USGS GNIS; rivers from USGS NHDPlus HR; rock from the USGS State Geologic Map Compilation.
A raindrop that lands in Armstrong reaches the Gulf of America by way of Mineral Bayou, the Blue River, the Red River, the Atchafalaya and the Lower Atchafalaya: about 800 river miles.
610 miles of the trip are on the Red River.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Armstrong; river miles along the main stem, rounded.
